The relationship between the activation of the vasopressin system and central hemodynamics in heart failure (including right and left heart filling pressures and cardiac output) is not clear. The investigators intend to examine the correlation between levels of copeptin and vasopressin and the central hemodynamic system in patients with advanced (class III or IV) heart failure. The investigators also aim to examine the relationship of selected cardiac biomarkers in blood and urine with cardiac filling pressures and cardiac output in patients with decompensated heart failure.